Hologram recording/reproducing apparatus

Abstract

A hologram recording/reproducing apparatus includes: a coherent light source; a spatial light modulator which spatially modulates light from the coherent light source; a Fourier transform lens which concentrates light modulated by the spatial light modulator upon a hologram medium; and a two-dimensional light-receiving element array which receives light from the hologram medium. The spatial light modulator is divided into a reference light area and a signal light area, and the divergence angle of reference light emitted from the reference light area is wider than the divergence angle of signal light emitted from the signal light area.

1. A hologram recording/reproducing apparatus, comprising:
 a coherent light source; 
 a spatial light modulator which spatially modulates light from the coherent light source; 
 a Fourier transform lens which concentrates light modulated by the spatial light modulator upon a hologram medium; and 
 a two-dimensional light-receiving element array which receives light from the hologram medium, wherein: 
 the spatial light modulator is divided into a reference light area and a signal light area; 
 the divergence angle of reference light emitted from the reference light area is wider than the divergence angle of signal light emitted from the signal light area; 
 the reference light area and the signal light area are each divided into a plurality of pixels, each pixel having an aperture; and 
 the aperture of each pixel of the reference light area is smaller than the aperture of each pixel of the signal light area. 
 
     
     
       2. The hologram recording/reproducing apparatus according to  claim 1 , wherein each pixel of the reference light area is smaller than each pixel of the signal light area. 
     
     
       3. The hologram recording/reproducing apparatus according to  claim 2 , wherein the length of each pixel of the reference light area is one-nth (n is an integer) the length of each pixel of the signal light area. 
     
     
       4. The hologram recording/reproducing apparatus according to  claim 1 , further comprising:
 a diffusion plate adjacent to the spatial light modulator; 
 wherein a diffusion angle of the diffusion plate opposite to the reference light area is wider than a diffusion angle of the diffusion plate opposite to the signal light area. 
 
     
     
       5. The hologram recording/reproducing apparatus according to  claim 4 , wherein:
 the diffusion plate is divided into a plurality of pixel areas each of which gives a different phase shift to light passing through the pixel areas; and 
 each pixel of the spatial light modulator corresponds to one pixel area of the diffusion plate in the signal light area, and each pixel of the spatial light modulator corresponds to a plurality of pixel areas of the diffusion plate in the reference light area. 
 
     
     
       6. The hologram recording/reproducing apparatus according to  claim 4 , wherein:
 the spatial light modulator includes at least one transparent substrate for sealing a liquid-crystal layer; 
 the transparent substrate has an uneven surface which functions as the diffusion plate; and 
 the diffusion angle of the uneven surface opposite to the reference light area is wider than the diffusion angle of the uneven surface opposite to the signal light area. 
 
     
     
       7. The hologram recording/reproducing apparatus according to  claim 6 , wherein:
 the uneven surface includes a rectangular uneven surface; and 
 the unevenness width and/or height of the uneven surface opposite to the reference light area is smaller than the unevenness width and/or height of the uneven surface opposite to the signal light area. 
 
     
     
       8. The hologram recording/reproducing apparatus according to  claim 6 , wherein:
 the uneven surface includes a smooth uneven surface; and 
 the granularity of the uneven surface opposite to the reference light area is smaller than the granularity of the uneven surface opposite to the signal light area. 
 
     
     
       9. The hologram recording/reproducing apparatus according to  claim 1 , wherein the spatial light modulator holds a fixed modulation pattern in the reference light area. 
     
     
       10. The hologram recording/reproducing apparatus according to  claim 1 , wherein:
 the spatial light modulator includes at least one transparent substrate for sealing a liquid-crystal layer; 
 the transparent substrate has an uneven surface which functions as a diffusion plate; and 
 the diffusion angle of the uneven surface opposite to the reference light area is wider than the diffusion angle of the uneven surface opposite to the signal light area. 
 
     
     
       11. The hologram recording/reproducing apparatus according to  claim 10 , wherein:
 the uneven surface of the transparent substrate is divided into a plurality of pixel areas each of which gives a different phase shift to light passing through the pixel areas; and 
 each pixel of the spatial light modulator corresponds to one pixel area of the uneven surface of the transparent substrate in the signal light area, and each pixel of the spatial light modulator corresponds to a plurality of pixel areas of the uneven surface of the transparent substrate in the reference light area. 
 
     
     
       12. The hologram recording/reproducing apparatus according to  claim 10 , wherein:
 the uneven surface includes a rectangular uneven surface; and 
 the unevenness width and/or height of the uneven surface opposite to the reference light area is smaller than the unevenness width and/or height of the uneven surface opposite to the signal light area. 
 
     
     
       13. The hologram recording/reproducing apparatus according to  claim 10 , wherein:
 the uneven surface includes a smooth uneven surface; and 
 the granularity of the uneven surface opposite to the reference light area is smaller than the granularity of the uneven surface opposite to the signal light area. 
 
     
     
       14. A hologram recording/reproducing apparatus, comprising:
 a coherent light source; 
 a spatial light modulator which spatially modulates light from the coherent light source; 
 a Fourier transform lens which concentrates light modulated by the spatial light modulator upon a hologram medium; and 
 a two-dimensional light-receiving element array which receives light from the hologram medium, wherein: 
 the spatial light modulator is divided into a reference light area and a signal light area; 
 the divergence angle of reference light emitted from the reference light area is wider than the divergence angle of signal light emitted from the signal light area; 
 the reference light area and the signal light area are each divided into a plurality of pixels; 
 said hologram recording/reproducing apparatus further comprises a micro-lens array which includes a plurality of element lenses corresponding to the plurality of pixels and which is adjacent to the spatial light modulator; and 
 the focal length of each element lens of the micro-lens array opposite to the reference light area is shorter than the focal length of each element lens of the micro-lens array opposite to the signal light area. 
 
     
     
       15. The hologram recording/reproducing apparatus according to  claim 14 , wherein:
 the spatial light modulator includes at least one transparent substrate for sealing a liquid-crystal layer; 
 the transparent substrate has a convex curved-surface part which functions as an element lens of the micro-lens array; and 
 the focal length of the convex curved-surface part opposite to the reference light area is shorter than the focal length of the convex curved-surface part opposite to the signal light area. 
 
     
     
       16. A hologram recording/reproducing apparatus, comprising:
 a coherent light source; 
 a spatial light modulator which spatially modulates light from the coherent light source; 
 a Fourier transform lens which concentrates light modulated by the spatial light modulator upon a hologram medium; and 
 a two-dimensional light-receiving element array which receives light from the hologram medium, wherein: 
 the spatial light modulator is divided into a reference light area and a signal light area; 
 the divergence angle of reference light emitted from the reference light area is wider than the divergence angle of signal light emitted from the signal light area; 
 the spatial light modulator includes a first liquid-crystal layer which modulates the intensity of light and a second liquid-crystal layer which modulates the phase of light; 
 the second liquid-crystal layer is divided into a reference-light-area liquid-crystal layer located in the reference light area and a signal-light-area liquid-crystal layer located in the signal light area; and 
 a variation in the phase of light at the reference-light-area liquid-crystal layer is larger than a variation in the phase of light at the signal-light-area liquid-crystal layer.